It's not like Obama decided this.
The structure of cost-of-living increases has been built into Social Security law since 1975. The formula, according to the SSI: "a COLA is equal to the percentage increase in the Consumer Price Index for Urban Wage Earners and Clerical Workers (CPI-W) from the third quarter of one year to the third quarter of the next. If there is no increase, there is no COLA."
It's a pretty big stretch to blame Obama for an automatic effect of deflation.
The good news is that the level of income subject to Social Security also won't increase.